1. Field of the Invention
The present invention relates to a mold structure for packaging LED chips and a method thereof, and particularly relates to a mold structure and a method for preventing package resins from overflowing on a rear face of a substrate of the LED chips.
2. Description of the Related Art
Referring to FIGS. 1 and 2, a known mold structure m includes a top mold 1a and a bottom mold 2a mated with the top mold 1a. The bottom mold 2a has a plurality of receiving spaces 20a of a larger size.
Referring to FIG. 3, a substrate 3a is etched to form a plurality of chip carrying areas 30a and a plurality of positive contact pins 300a and negative contact pins 301a that correspond to the chip carrying areas 30a. 
Moreover, a plurality of LED chips 4a is arranged on the corresponding chip carrying areas 30a, respectively. In addition, a positive pole and a negative pole (not shown) of each LED chip 4a are electrically connected with the corresponding positive contact pin 300a and negative contact pin 301a via leading wires 40a by a wire-bounding method. Furthermore, the LED chips 4a are divided into a plurality of LED chip areas. Each LED chip area has a plurality of LED chips 4a arranged in a matrix shape. For example, in the FIG. 3 each LED chip area has a 5*5 LED chip matrix.
Referring to FIG. 4, before the substrate 3a is arranged under the top mold 1a, a self-adhesive tape 5a is attached on a rear face of the substrate 3a. 
Referring to FIG. 5, after the top mold 1a and the bottom mold 2a are mated together and package resins 6a are poured into the receiving spaces 20a, the substrate 3a is deformed easily and the package resins 6a overflow easily on the rear face (as shown by the arrows in FIG. 5) of the substrate 3a due to thermal expansion and pressure concentration (because the size of the receiving space 20a is larger). Hence, the know mold structure not only wastes package resins but it is difficult to clean the package resins that overflow on the substrate.
Moreover, the prior art still some other defects, as follows:
1. The cost of the self-adhesive tape 5a is high, and the prior art needs to use a precision adhesion instrument to adhere the self-adhesive tape 5a on the rear face of the substrate 3a. 
2. The LED chips 4a are too close to each other, so that the structural strength of the LED chip package is inadequate.
3. Because the size of the receiving spaces is larger, the packaged LED chips 4a are difficult to separate from the bottom mold 2a. Therefore, the yield rate of the pattern draw is decreased.